This invention relates to septic systems and, more particularly, to drop boxes for use in septic systems, including improved seal means used at the invert openings of such drop boxes.
The known prior art drop boxes comprise a box-shaped concrete structure having pairs of invert openings formed on respective opposing sidewalls thereof; typically the inflow and outflow drain tile openings are 6 to 8 inches higher than the lateral drain tile openings. Once the typical four inch diameter drain pipes are inserted through such invert openings, concrete mortar or grout, for example, is used to seal off the pipes against the drop box's sidewalls to prevent leakage. A generally planar concrete lid is used to cover an installed drop box, whereupon the box and lid are backfilled over to form part of a septic field system.
In use, such prior art drop boxes have many disadvantages, including the effects of movements of the respective drainage pipes relative to the drop box due to settling of backfill over time, as well as expansion and contraction due to temperature variations. Such movements cause leaks to occur at the grouted joints where the drain pipes extend through the drop box invert openings. Further, since the lids used with prior art drop boxes simply rested on top of the drop box, they oftentimes were inadvertently scraped off of the box, such as during landscaping preparations for the construction site. Further, due to the use of concrete, such prior art drop boxes often crumbled and otherwise disintegrated over time thereby limiting their useful life. The corrosive solutions present in most septic tank systems also acted to deteriorate concrete-type drop boxes.
Although neoprene and other rubber-type seals have been used for certain construction installations, such as with vent stacks extending through residential roof structures or with cast iron pipes used in certain plumbing applications, such alternate sealing arrangements have not proved satisfactory for use with septic drop boxes. Further, while there are numerous seal structures utilized to seal relatively large diameter water and sewer tiles to manholes, none have proved satisfactory for adaptation to septic drop boxes nor are readily usable in the field.